In the production of gasoline powered ac generators or the like, it is highly desirable to provide precise voltage regulation, and to provide good motor starting ability. Commercially this is often done utilizing a power transformer. Commercial generators produced utilizing a power transformer to regulate the output voltage, however, typically have regulated output voltage to about .+-.4%, and motor starting ability is about 0.35 hp/kw. These values are less than desired.
According to the present invention, an electronic voltage regulator is provided which utilizes generator field control for regulating the output voltage of an ac generator while improving motor starting ability. The electronic voltage regulator according to the present invention produces the desired results in an efficient and cost effective manner with a minimum number of components. Utilizing the invention it is possible to regulate the output voltage of the generator so that it is about .+-.0.8%, and to provide a motor starting ability of about 0.75 hp/kw.
According to the present invention, an electronic voltage regulator is provided for an ac electric generator having a field, output voltage and frequency. First means are provided for producing a filtered dc representation of the generators output voltage. Second means are provided for producing a dc voltage which is proportional to the frequency of the generator. Third means are provided for comparing the dc voltages produced by the first and second means, and a fourth means are provided for using a comparison of the voltages to control the generator field and thereby regulate the output voltage of the generator.
The means for producing the filtered dc representation of the output voltage includes means for sensing the output voltage, rectifying it to dc, and filtering it to obtain a relatively smooth dc voltage, which is directly proportional to the output voltage of the generator. A small amount of ripple voltage is provided.
The means for producing a dc voltage which is proportional to the frequency of the generator comprises novel circuitry itself. The circuitry includes means for sensing the frequency of the ac output voltage including a resistor and a pair of back-to-back zener diodes, to produce a square wave. The circuitry further comprises means for producing a dc voltage proportional to the sensed frequency, which means comprises a high pass RC filter for differentiating the square wave to produce a constant amplitude pulse, means for rectifying the pulse to dc, and an RC network for averaging it. The circuitry further comprises means for amplifying this dc voltage and clamping it so that up to a maximum sensed frequency the small dc voltage produced is proportional to the sensed frequency, but does not increase above that maximum. Such means includes an integrated circuit operational amplifier which has a zener diode to clamp maximum of the voltage.
The means for comparing the dc voltages produced by the first and second means includes an operational amplifier comparator circuit. This circuit has a small amount of hysteresis so that the output of the comparator switches on and off in synchronization with the small ripple voltage from the first means.
The fourth means, for using the comparison of the dc voltages to control the generator field, comprises a power stage which amplifies the switching signal from the comparator to a level which can control the field current. The power stage is powered by a separate winding on the generator which is rectified to dc and filtered by a large capacitor, this voltage then being applied directly to the generator field in a controlled manner by the output by the comparator. Thus, as load is applied to the generator the ac output voltage will tend to decrease. This decrease is sensed by the voltage sensing circuitry and causes the duty cycle of the comparator stage to increase. This in turn causes the generator's field current to increase. The increase in field current compensates for the additional load and tends to maintain the generators ac output voltage constant (e.g. within about .+-.0.8%).
It is the primary objecty of the present invention to provide a simple and effective electronic voltage regulator for an ac electric generator and effective circuitry for producing an amplified dc voltage in response to sensed frequency, associated therewith. This and other objects of the invention will become clear from an inspection of the detailed description of the invention, and from the appended claims.